1. Technical Field
This invention relates to a method and apparatus to estimate a capacitance in a battery. More specifically, a process for calculating time remaining for operation of a battery operated device.
2. Description of the Prior Art
Many electronic devices today require electrical power for operation. Some of these devices are connected to conventional AC power supplies. However, in recent years laptop computers and personal digital assistants have become popular. These type of portable devices, as well as other devices that require a power supply for operation, require portable power sources, such as batteries, for operation when an AC power supply is not available. Power failure associated with such devices may result in loss of data or other failure of the device. Therefore, it is necessary to have information regarding the remaining power supply or battery life available from a specific battery while in use in an electronic device. It is desirable that the device provide an indication to the operator when power remaining from the power supply is insufficient to continue operation of the device, so that the operator may have a sufficient amount of time to save their data and properly shut-down operation of the device.
Recent developments in battery technology include the use of a discharge control circuit that serves to estimate the voltage drop of a battery based upon the current output of electrical power from the battery. The discharge control circuit is incorporated within the battery. By incorporating the discharge control circuit within the battery, the costs associated with the manufacture of the battery, as well as the overall size of the battery, are increased. Other prior art solutions include the use of battery type detectors and temperature sensors within the device utilizing the battery as a means of estimating battery life. There are shortcomings associated with the prior art solutions for providing an accurate calculation of time remaining on a battery for proper operation of a battery powered device. In general, the solutions to date require an added expense in either the manufacture of the battery, such as a discharge control circuit, or in the battery powered device, such as the incorporation of temperature sensors. Accordingly, it is desirable to provide a solution that enables the battery operated device to operate with either conventional batteries or “smart” batteries (i.e. batteries that incorporate technology such as the discharge control circuit) while still providing an accurate calculation of the time remaining for operation of the device with the current battery supply.